1. Field of the Invention
The present invention relates to an apparatus for controlling an internal combustion engine which emits exhaust gases through a catalytic converter, and more particularly to an apparatus for controlling an internal combustion engine to accelerating a temperature increase and activation of a catalytic converter when the internal combustion engine is idling after it has started to operate.
2. Description of the Related Art
Catalytic converters such as three-way catalytic converters are disposed in the exhaust systems of internal combustion engines for purifying exhaust gases emitted from the internal combustion engines. Generally, such a catalytic converter cannot maintain a desired ability to purify exhaust gases unless its temperature rises to a level to activate the catalytic converter. It is, therefore, important for the catalytic converter to achieve a desired level of exhaust gas purification immediately after the internal combustion engine has started to operate when the temperature of the catalytic converter is comparatively low.
The applicant of the present application has proposed a technology for purifying exhaust gases when the catalytic converter has a relatively low temperature, as disclosed in Japanese laid-open patent publication No. 10-299631, Japanese laid-open patent publication No. 11-210608, and U.S. patent application Ser. No. 09/063732. The proposed exhaust gas purifying system will be described below.
When an internal combustion engine idles initially after it has started to operate, the opening of the throttle valve or a control valve in a bypass passage that bypasses the throttle valve (these valves will hereinafter collectively be referred to as a "flow control valve") is controlled so as to make the amount of intake air introduced into the combustion chamber of the internal combustion engine, greater than when the internal combustion engine idles normally, e.g., when the internal combustion engine idles after an automobile propelled by the internal combustion engine has traveled. Furthermore, after the amount of intake air has started increasing, the ignition timing of the internal combustion engine is controlled under feedback control in order to converge the rotational speed (actual rotational speed) of the internal combustion engine, which tends to increase due to the increasing amount of intake air, toward a certain target rotational speed, so that the ignition timing will be more retarded than normal.
When the amount of intake air is increased and the ignition timing is retarded, the exhaust gases emitted by the internal combustion engine have a greater amount of heat, and hence the catalytic converter heated by the exhaust gases is activated quickly. As a result, the catalytic converter is capable of achieving a desired purification ability quickly after the internal combustion engine has started to operate.
At the same time, the ignition timing is feed-back-controlled to converge the rotational speed of the internal combustion engine, which is liable to increase as a result of an increase in the amount of intake air, to the target rotational speed, so that the rotational speed of the internal combustion engine can be kept stably at an optimum rotational speed.
For increasing the amount of intake air, a command value for the opening of the flow control valve is generated in order to give the catalytic converter an amount of heat capable of sufficiently increasing the temperature of and activating the catalytic converter within a predetermined period of time after the internal combustion engine has started to operate, and also to operate the internal combustion engine after it has started to operate under as smooth and good fuel combusting conditions. The opening of the flow control valve is controlled by an actuator or the like based on the command value. Heretofore, it has been customary to understand that the actual opening of the flow control valve and the actual amount of intake air introduced into the internal combustion engine are determined uniquely by the command value for the opening of the flow control valve, determine a magnitude and a time-depending change of the command value for the opening of the flow control valve according to a data table or the like in a feed-forward fashion, and control the opening of the flow control valve according to the command value.
However, behaviors of the flow control valve or the intake system of the internal combustion engine which includes the flow control valve generally vary from product to product and also suffer time-dependent characteristic variations. Because of such behavioral variations and time-dependent characteristic variations, even when the opening of the flow control valve is controlled according to a command value determined in a feed-forward manner, the amount of intake air actually drawn into the combustion chamber of the internal combustion engine varies from product to product or suffer time-dependent variations. Therefore, the amount of heat of exhaust gases emitted from the internal combustion engine upon combustion of an airfuel mixture which comprises intake air and fuel at a given ratio also varies from product to product or suffer time-dependent variations. As a result, the temperature-increasing characteristics of the catalytic converter to which the heat of the exhaust gases is applied also suffer variations, with the result that it may not be possible to appropriately increase the temperature of and activate the catalytic converter within a given period of time.